Recent studies have demonstrated that hepatitis C virus (HCV) is closely related with hepatocellular carcinoma in Japan. Although positive rate for antibody against HCV in the United States is nearly same as that in Japan, the occurrence rate of hepatocellular carcinoma in the United States is smaller than that in Japan. To understand the difference between the United States and Japan, we compared sequences of HCV obtained from Japanese patients with those from the United States.We obtained HCV-cDNA from a patient with hepatocellular carcinoma. It has 90.7-91.4% homology in nucleotide sequences of two isolates obtained in Japan while 78.4-78.8% with two isolates obtained in the United States. Those three isolates from Japan were classified into Japanese-type (type II, Okamoto) and three from United States into American-type (type I, Oakamoto). When we classified 38 patients with chronic hepatitis C treated with Interferon, 28 (75%) were Japanese-type. On the other hand, only 7 (21%) out of 33 patients in the United States were Japanese-type.These findings suggest that there are at least two types of HCV in Japan and United States and a type which is major in Japan is not common in the United States. Further studies are necessary to elucidate the possible role of the difference of HCV strains on the difference of prevalence of prevalence in hepatocellular carcinoma in both countries.